A photovoltaic (PV) power generation system for supplying electricity to an electric power grid includes an array of PV panels and an inverter. A PV array may include just a few PV panels, for example a PV power generation system for supplying electric power to a residence or small commercial establishment, or may have many thousands of panels as in a utility-scale PV array. The voltage and current output from each of the PV panels in the PV array are combined in an electrical circuit and input to the direct current (DC) input of the inverter, which converts the combined DC electrical power from the PV panels into alternating current (AC) electrical power output having an AC voltage suitable for connection to the electric power grid. DC output voltage from the PV array, corresponding to DC input voltage to the inverter, must be within a specified DC input voltage range for the inverter's AC output voltage to be within an acceptable range for connection to the electric power grid.
A reduction in DC output voltage from one or more PV panels in a PV array may cause voltage at the DC input to the inverter to be lower than the inverter's specified minimum DC input voltage, causing a related reduction in the inverter's AC output voltage. A system operator or automatic control system may therefore choose to exclude the power output from a PV panel with low DC output voltage from the inverter input in order for other PV panels with sufficiently high output voltage to maintain a desired output voltage from the inverter, at the expense of reducing the total amount of electrical power produced by the PV array. As the number of PV panels with low output voltage increases, for example when cloud shadows move across the PV array or when the sun sets, the number of PV panels contributing an acceptable magnitude of input voltage to the inverter decreases, and power output from the PV array decreases. For a PV array comprising PV panels known in the art, it is eventually necessary to isolate the PV array from the inverter input rather than output AC power at too low a voltage for supplying the electric power grid, even though the PV array is still generating some electrical power.
In addition to reductions in incident radiation from cloud shadows and the daily motion of the sun, PV panel output voltage may also be reduced by, for example, dirt or water on the panel surface, airborne obstructions to solar radiation such as precipitation, smoke, smog, and dust, and shadows from nearby trees or buildings. PV panel voltage also decreases when solar cells in the panel are subjected to high temperatures. Aging effects or an electrical fault within a PV panel may also contribute to a reduction in output voltage. A properly functioning PV panel outputs electrical power as long as a sufficient amount of illumination is incident upon the panel, but as the incident illumination decreases, the output voltage also decreases. PV panel output power with insufficient voltage for coupling into an inverter represents lost power and reduced power generating efficiency.
What is needed is a system for reconfiguring electrical connections between PV panels in a PV array to control electrical power produced under conditions of reduced illumination. What is further needed is a system for reconfiguring electrical connections between PV panels so that a magnitude of DC electrical voltage at a power output from a PV array is greater than or equal to the minimum DC input voltage for an inverter.